1. Field of the Invention.
This invention relates to a process for the production of linear amorphous polyamides, which comprises condensing an aqueous solution of salts comprising at least one aromatic diacid and a greater than equimolar amount of at least one aliphatic diamine, wherein the resulting polyamides have more amine endgroups than acid endgroups. This invention also relates to linear amorphous polyamides as described above. These polyamides are typically clear and exhibit a good balance of toughness and processability. They can be used for medical, electrical, and cosmetic applications.
2. Description of the Prior Art
Polyamides prepared from dicarboxylic acids (diacids) and diamines are known. In particular, polyamides prepared from equimolar amounts of either aliphatic diacids and aliphatic diamines or aromatic diacids and aliphatic diamines are known. Depending on their composition, these polyamides are either crystalline or amorphous. They may be prepared by known processes, for example, by condensing an aqueous salt solution of equimolar amounts of diacid and diamine monomers, optionally, compensating for losses of diamine occurring during the condensation reaction by adding or using an excess of diamine. The use of a diamine in amounts greater than anticipated to compensate for loss during the condensation reaction has been known to cause reaction mixture cross-linking during production.
Polyamides prepared from equimolar amounts of aromatic diacids, such as isophthalic acid and/or terephthalic acid and aliphatic diamines, in addition to amounts of diamine monomer sufficient to compensate anticipated processing losses, tend to be notably more viscous and less easily processed than polyamides prepared from aliphatic diacids and diamines. In extreme cases, these polyamides are cross-linked and, therefore, unprocessable.
It is generally known that aromatic diacids, such as isophthalic acid and terephthalic acid, polymerize more slowly than the standard aliphatic diacids used to make nylon 66, 69, 610, or 612. It is believed that the slower polymerization rate allows competing degradation reactions to become more significant. It is also believed that these degradation reactions lead to branching in the polyamide molecule, thereby resulting in a decrease in or loss of processability.
It is therefore an object of the present invention to provide a process for the production of linear amorphous polyamides prepared from aromatic diacids and aliphatic diamines, wherein the resulting polyamides exhibit a good balance of properties, including good processability.
It is a further object of the present invention to provide linear amorphous polyamides as described hereinabove.